I see my iPhone 11 Pro Max in Finder & in Music but get "The selected device could not be found" error when I click on it
This is exceedingly frustrating, but I have the latest macOS Big Sur 11.2.3 update installed on my Mac Mini (Late 2014) and the latest iOS 14.4.1 update installed on my iPhone 11 Pro Max. This problem existed before these latest updates, but nothing has changed since. When I plug in and unlock my iPhone, I can see it in Finder under the "Locations" section, and under "Devices" on the Music app, so clearly these applications and my Mac recognize my iPhone. But when I click on it I get the error, "The selected device could not be found".
In my Music app on the Mac, I'm also seeing approximately 50% of my music, which includes music I had uploaded, not just music I purchased in iTunes, greyed out with a "Cloud Status" that says "Waiting" as though it's syncing...except it's not.
I first went through Apple Support txt edition, then they set me up for phone support. Neither person was much help here despite trying lots of things. Neither seemed like a great troubleshooter though, so my confidence that someone on a helpline can help me here is quite low. Now throwing a Hail Mary here, in hopes that someone has a clue what's going wrong here and how to fix it.
Thankful in advance for any knowledgeable person's consideration and thoughts on this.
Mac mini 2018 or later